This invention relates to the deodorization and purification of L-aspartyl-L-phenylalanine alkyl esters. L-Aspartyl-L-phenylalanine alkyl esters, having from 1 to 3 carbon atoms in the alkyl group, especially the methyl ester, are useful as sweetening agents. One desirable method for preparing such esters is by the reaction of L-aspartic acid N-thiocarboxyanhydride and an appropriate L-phenylalanine alkyl ester in aqueous solution, for example, in accord with the general procedures described in J. Org. Chem. 36, 49 (1971). However, this method suffers from the disadvantage that small amounts of certain impurities are formed in this reaction by undesired side reactions or degradation of species in the reaction mixture, which impart an unpleasant odor to the L-aspartyl-L-phenylalanine alkyl ester produced. Such odorous impurities are not removed in conventional procedures for the recovery and purification of the desired ester, such as recrystallization or the removal of amino acid impurities by chromatographic methods, and are present in the otherwise purified crystalline product. The unpleasant odor associated with the presence of these impurities is particularly undesirable in view of the intended use of the L-aspartyl-L-phenyl-alanine alkyl esters as sweetening agents for foodstuffs and beverages and development of a commercially acceptable sweetening agent for such use requires removal of the undesired malodorous impurities. Such impurities may also adversely affect the taste quality of products containing these sweetening agents.